The present invention relates to a method and apparatus for controlling the steplessly variable transmission ratio of a continuously variable transmission, especially of a cone disk belt transmission in a motor vehicle, in which desired values are specified to a power output control device of the driving engine by means of a drive pedal, in which desired rotational speed values dependent on the position of the drive pedal are compared in a control apparatus with the actual rotational speed values of the driving engine and in which, dependent on the difference of the two rotational speed values, a rapid change of the transmission ratio is activated by the control apparatus by way of an adjusting mechanism in case of a large difference and a slower change of the transmission ratio is activated in case of a difference of the two rotational speed values which becomes smaller, whereby the change of the transmission ratio is terminated with a disappearing difference.
A method and apparatus of the aforementioned type can be ascertained from the operation of a control arrangement for a cone disk belt transmission as disclosed in the DE-OS 35 04 763.
This method is based on a regulation of the engine rotational speed to desired values specified by the drive pedal of the motor vehicle by adjustment of the split cone disks of the stepless transmission.
The regulating deviation is thereby dependent on the desired rotational speed values and measured actual rotational speed values of the combustion engine or on the transmission input shaft and of further measured values.
It has been found that with such an engine rotational speed regulation, transitions from one engine rotational speed to another, for example, for the acceleration of the vehicle, whereby the desired rotational speed specification is raised suddenly by the drive pedal, is terminated as a rule only after an over-shooting of the actual rotational speed beyond the new desired rotational speed. This over-shooting results from an excess torque of the engine compared to the torque desired at the transmission input at the instant, in which the engine actual rotational speed has reached the new desired value.
The acceleration or revving up of the engine is effected by adjustment of the transmission ratio into the short range (transmission input rotational speed &gt;&gt; output rotational speed). If the engine rotational speed has reached its desired value, then the transmission ratio is again adjusted into a longer range.
The acceleration or revving up of the engine can thereby take place in an uncontrolled manner because the transmission cannot be adjusted so rapidly that the rotational speed-overshooting is avoided. With a rapid reaction of the transmission control to the overshoot rotational speeds, the engine is strongly decelerated to the desired rotational speed; a steep torque increase at the transmission output takes place thereby by reason of the reduction of the kinetic engine energy, which similar to a shifting jerk or jolt in automatic change-speed transmissions becomes effective in a negative manner for the driving comfort.
Other disadvantages of the rotational speed overshoot are a high noise emission, an unnecessary increased fuel consumption as well as power output collapses in diesel engines when reaching the down-regulating curve.
The DE-OS No. 35 04 763 teaches that the adjustment of the transmission ratio is to take place rapidly with a large desired-actual rotational speed deviation and is to take place more slowly when the deviation becomes smaller; however, this prior art disclosure contains no indication in what direction the adjustment is to be made and how the adjusting velocity will be controlled.
An arrangement for the regulation of the actuating force of a shifting member in automatically shifted change-speed transmissions is known from the DE-PS No. 21 24 024, which has the task, when shifting-up the change-speed transmission, to minimize the shifting periods, temperature increases and load of the force-locking friction elements with smallest possible shifting jerk.
The regulating magnitude in this arrangement is a difference of the actual value of the change per time of the transmission input rotational speed or engine rotational speed and of a desired value which depends on different measuring magnitudes (engine torque, transmission output rotational speed, vehicle load, transmission temperature, transmission ratio of engaged speed).
This desired or specified value is not equally large for all shifting operations even though it depends from some measuring magnitudes which are constant for short periods of time (temperature, load), but it always has a certain value differing from zero. This is also the case when according to a simplified proposed control modification, it is determined exclusively from the engine rotational speed at the beginning of the shifting-up operation--the desired value is then constantly free of variable influencing magnitudes and for the entire shifting operation.
This prior art arrangement is neither provided nor utilizable for the deliberate guidance of the engine rotational speed to a value specified by the drive pedal. Added thereto is the fact that differing from stepless transmissions, larger engine rotational speed band widths must be covered by change-speed transmissions with an unchanged transmission ratio, i.e., shifting or transmission ratio change operations cannot take place with every change of the drive pedal setting.
It is the object of the present invention to so improve the method applied by the arrangement of the aforementioned type that an overshooting of the engine rotational speed is prevented after reaching a changed desired rotational speed value while maintaining a high driving comfort, and to provide an arrangement for carrying out the method in accordance with the present invention.
The underlying problems are solved according to the present invention in that in the method according to the present invention, values representing the desired rate of change of engine rotational speed for the change per time of the engine rotational speed are unequivocally determined by means of at least one stored characteristic curve as a function of the difference of the desired and actual rotational speed values and are compared with determined values representing the actual rate of change of engine rotational speed and in that differences of the values representing the desired rate of change of engine rotational speed and actual values are fed to a controller as regulating deviations whose adjusting magnitude acts upon the adjusting mechanism for the control of the velocity of the change of the transmission ratio. With an apparatus according to the present invention, the signals representing the difference between the desired and actual engine rotational speed are fed to a signal input of a characteristic curve memory in the control apparatus, in the output of which desired rate of change of engine rotational speed signals coordinated to each rotational speed difference are present for the guidance of the change per time of the engine rotational speed with the change of the effective transmission ratio, in that the actual rotational speed signals are fed to a differentiating element for the formation of actual rotational speed change signals per time, and in that the desired and the actual rate of change of engine rotational speed signals are fed to a subtracting stage for the formation of the regulating deviation signals to be fed to the controller.
An uncontrolled speeding up (revving up) of the engine rotational speed during the adjustment of the transmission ratio is forcibly avoided by the specification of desired change values of the engine rotational speed in that that the difference between the desired and actual rotational speed is no longer used, but rather the difference between the specified and the actual change per unit time of the engine rotational speed, i.e., a difference of acceleration or deceleration values is used as regulating deviation and is fed to a controller.
The specification of the engine acceleration thereby takes place advantageously along a linear or non-linear characteristic curve which is plotted along a rotational speed axis or a desired-actual-rotational speed difference axis and intersects the former in the respective desired rotational speed point or the latter in its zero point.
A steady development of the desired rate of change of engine rotational speed thus results which has the value of zero exactly at the point of coincidence between desired and actual rotational speed. Comfortable transitions between individual engine rotational speed values are assured thereby.
Furthermore, either only the desired rotational speed specification by the drive pedal can be influenced or also an engine acceleration-specification characteristic line which corresponds to the drive range characteristic can be determined by means of a drive range selector switch which can preselect several forward driving ranges, for example,--"sporty, normal, consumption-optimized".
If in a vehicle with stepless transmission the drive pedal and the power output regulating device of the engine, i.e., for example, the throttle valve in the suction channel or the control rack of the diesel injection pump, are mechanically decoupled and the power output control device is controllable by way of an adjusting member from an engine performance graph memory (memory containing a set of engine characteristic curves), the engine torque can be raised in the case of application with the method according to the present invention by an engine load increase independent of the drive pedal if a higher desired rotational speed is demanded in the low rotational speed operation optimized for consumption. By the guidance of the engine acceleration along the specified characteristic curve, the engine then also cannot speed up (rev up) in an uncontrolled manner while the transmission ratio is adjusted for the acceleration of the vehicle. A possible torque collapse in the transmission output is thus compensated.